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From: James Kuyper <jameskuyper@alumni.caltech.edu>
Newsgroups: comp.lang.c
Subject: Re: question about nullptr
Date: Sun, 25 Aug 2024 23:45:46 -0400
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On 8/25/24 21:18, Keith Thompson wrote:
> James Kuyper <jameskuyper@alumni.caltech.edu> writes:
>> On 8/25/24 16:56, dave_thompson_2@comcast.net wrote:
>>> On Wed, 10 Jul 2024 11:09:41 -0400, James Kuyper
>>> <jameskuyper@alumni.caltech.edu> wrote:
>>>
>>>> NULL is required to expand
>>>> into a null pointer constant ... 0 and (void*)0 are the
>>>> two most likely and common choices.
>>>>
>>> ((void*)0)
>>> Otherwise NULL["foo"] gives quite the wrong result
>>
>> Correct. Sorry.
>
> A mostly meaningless price of trivia: In C17 and earlier, an excessively
> literal reading of the standard implies that ((void*)0) is not a null
> pointer constant. It says that a null pointer constant is "An integer
> constant expression with the value 0, or such an expression cast to type
> void *". It does not say that a parenthesized null pointer constant is
> a null pointer constant. (And (void*)0 is a null pointer constant but
> not a valid definition for NULL.)
>
> C23 fixes this by updating the wording for parenthesized expressions.
>
> C17: "A *parenthesized expression* is a primary expression. Its type and
> value are identical to those of the unparenthesized expression. It is an
> lvalue, a function designator, or a void expression if the
> unparenthesized expression is, respectively, an lvalue, a function
> designator, or a void expression."
>
> C23: "A *parenthesized expression* is a primary expression. Its type,
> value, and semantics are identical to those of the unparenthesized
> expression."

I remembered that you had raised this issue before, and I think my
memory of that issue is what led me to leave out the outer parentheses.
I'm glad to know that they cleared it up.